CN109980595B - Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit - Google Patents

Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit Download PDF

Info

Publication number
CN109980595B
CN109980595B CN201910374908.1A CN201910374908A CN109980595B CN 109980595 B CN109980595 B CN 109980595B CN 201910374908 A CN201910374908 A CN 201910374908A CN 109980595 B CN109980595 B CN 109980595B
Authority
CN
China
Prior art keywords
fault
current
voltage
charge
capacitor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN201910374908.1A
Other languages
Chinese (zh)
Other versions
CN109980595A (en
Inventor
付媛
江国文
张祥宇
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
North China Electric Power University
Original Assignee
North China Electric Power University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by North China Electric Power University filed Critical North China Electric Power University
Priority to CN201910374908.1A priority Critical patent/CN109980595B/en
Publication of CN109980595A publication Critical patent/CN109980595A/en
Application granted granted Critical
Publication of CN109980595B publication Critical patent/CN109980595B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/006—Calibration or setting of parameters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications

Landscapes

  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a method for determining fault clearing time of a flexible direct-current power grid under a bipolar short circuit. The method comprises the following steps: obtaining instantaneous values of the initial-stage voltage and current of the fault according to the initial values of the instantaneous direct-current voltage and the line current of the fault; respectively calculating the accumulated electric quantity of the fault current and the variable quantity of the electric charge carried by the capacitor caused by the charge and discharge of the bus voltage according to the instantaneous values of the initial voltage and the current of the fault; calculating the maximum variation of the charges carried by the capacitor during the fault according to the charge quantity carried by the capacitor at the steady-state operation point of the system and the charge quantity carried by the capacitor at the limit operation point of the system; according to the principle of equal electric quantity, when the accumulated electric quantity of the fault current is equal to the maximum variation of the electric charge carried by the capacitor during the fault, the fault clearing time of the system under the bipolar short-circuit fault is obtained. The method for determining the fault clearing time of the flexible direct-current power grid under the bipolar short circuit is beneficial to reducing the action requirement of a direct-current system on a circuit breaker and can also enhance the transient stability of the system.

Description

Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit
Technical Field
The invention relates to the technical field of fault analysis and protection of a flexible direct-current power grid, in particular to a method for determining fault clearing time of the flexible direct-current power grid under a bipolar short circuit.
Background
With the wide application of distributed energy and constant power load, the flexible direct current power grid becomes the key point of research and application at home and abroad depending on the advantages of the flexible direct current power grid. Compared with an alternating-current power distribution network, the flexible direct-current power grid has the advantages of simple conversion device, low cost and the like, and the influence of frequency mutation, power angle swing and other problems on the power quality does not need to be concerned. At present, measures for improving the voltage stability of the flexible direct current power grid are taken, wherein a controller is added, and a fault is quickly and effectively isolated by analyzing the fault characteristics of a system. However, the flexible direct-current power grid has low inertia, and after a bipolar short-circuit fault occurs, the system is seriously damaged by the large fluctuation or continuous oscillation of the direct-current bus voltage.
Disclosure of Invention
The invention provides a method for determining fault clearing time of a flexible direct-current power grid under a bipolar short circuit, which is beneficial to reducing the action speed requirement of a direct-current system on a circuit breaker and enhancing the transient stability of the system.
In order to achieve the purpose, the invention provides the following scheme:
a method of determining fault clearing time of a flexible direct current power grid under a bipolar short circuit, the method comprising:
obtaining instantaneous values of the initial-stage voltage and current of the fault according to the initial values of the instantaneous direct-current voltage and the line current of the fault;
respectively calculating the accumulated electric quantity of the fault current and the variable quantity of the electric charge carried by the capacitor caused by the charge and discharge of the bus voltage according to the instantaneous values of the initial voltage and the current of the fault;
calculating the maximum variation of the charge carried by the capacitor during the fault according to the charge quantity carried by the capacitor at the steady-state operation point of the system and the charge quantity carried by the capacitor at the limit operation point of the system;
according to the relation between the charge quantity of the capacitor on the direct current side after the fault and the charge and discharge of the bus voltage, an equal-electric quantity principle is provided, and according to the equal-electric quantity principle, when the accumulated electric quantity of the fault current is equal to the maximum variation quantity of the charge of the capacitor during the fault, the direct current voltage operating point falls to a limit voltage point, and the fault clearing time of the system under the bipolar short-circuit fault is obtained.
Optionally, the obtaining instantaneous values of the initial fault voltage and current according to the initial values of the instantaneous fault dc voltage and the line current specifically includes:
discharge equation based on DC capacitance
Figure BDA0002051292050000021
Solving the second order differential equation to obtain a pair of conjugate complex roots:
Figure BDA0002051292050000022
wherein
Figure BDA0002051292050000023
According to initial values of the fault instant direct current voltage and the line current, instantaneous values of the fault initial voltage and the fault initial current are obtained as follows:
Figure BDA0002051292050000024
wherein
Figure BDA0002051292050000025
In the formula, A, beta and theta are constant parameters in a fault initial-stage voltage and current instantaneous expression, sigma and w' are constant parameters in a conjugate complex root of a direct-current capacitance discharge equation, and UbAnd IbFor initial values of the fault instantaneous DC voltage and line current, R0And L0And C is a parallel capacitance value of the direct current side for fault equivalent impedance.
Optionally, the method of calculating the accumulated electric quantity of the fault current and the variation of the electric charge carried by the capacitor due to the charging and discharging of the bus voltage according to the instantaneous values of the initial fault voltage and the current includes:
according to the formula
Figure BDA0002051292050000026
Calculating the variable quantity of the charges carried by the capacitor caused by the charge and discharge of the bus voltage;
according to the formula
Figure BDA0002051292050000031
Calculating the accumulated electric quantity of the fault current;
in the formula ucFor instantaneous voltage value at initial stage of fault, t0Time of occurrence of a failure, t1At the time of the fault removal, Δ i is a valid integrated value of the current during the fault.
Optionally, the obtaining the maximum variation of the charge carried by the capacitor during the fault according to the charge carried by the capacitor at the steady-state operation point of the system and the charge carried by the capacitor at the limit operation point of the system specifically includes:
according to formula Q1＝CUbCalculating capacitance of a system at steady state operating pointThe amount of charge carried by the device;
according to formula Q2＝CUcmaxCalculating the charge quantity carried by the capacitor at the limit operating point of the system;
according to the formula Δ Q1max＝Q1-Q2Calculating the maximum variation of the charge carried by the capacitor during the fault;
in the formula of UbFor an initial value of the fault instantaneous DC voltage, UcmaxThe voltage is the limit operating point voltage, and C is the parallel capacitance value of the direct current side.
Optionally, the method includes the steps of providing an "equal-electric-quantity principle" according to a relation between charge quantity carried by a capacitor on a dc side after a fault and bus voltage charge and discharge, and dropping a dc voltage operating point to a limit voltage point according to the "equal-electric-quantity principle" when accumulated electric quantity of fault current is equal to a maximum variation of charge carried by the capacitor during the fault, so as to obtain fault clearing time of the system under the bipolar short-circuit fault, which specifically includes:
fault transient voltage equation, current equation and change Q of charge of capacitor from fault occurrence time to limit cut-off timemaxCan be simplified to be represented as:
Figure BDA0002051292050000032
wherein
Figure BDA0002051292050000033
Will be the equation
Figure BDA0002051292050000041
After the relevant fractional integral conversion is carried out, the fault clearing time of the system under the bipolar short-circuit fault is obtained as follows:
Figure BDA0002051292050000042
in the formula
Figure BDA0002051292050000043
A system for determining fault clearing time of a flexible direct current power grid under a double-pole short circuit comprises a power frequency three-phase alternating current power supply, wherein an output end of the power frequency three-phase alternating current power supply is connected into a direct current bus through an alternating current circuit breaker, a filter, a transformer and a power supply type converter VSC1 in sequence, and the direct current bus is connected with a direct current load through a power supply type converter VSC 2.
Optionally, the power converter VSC1 is a unidirectional AC/DC converter, and the power converter VSC2 is a bidirectional DC/DC converter.
Compared with the prior art, the technology has the following beneficial effects:
the invention provides a method for determining fault clearing time of a flexible direct current power grid under a bipolar short circuit, which aims at the voltage stability problem of the flexible direct current power grid, combines the transient recovery rule of direct current bus voltage after the bipolar short circuit fault of a system, and utilizes the principle of equal electric quantity, namely in the direct current power grid, the change quantity delta Q of charges carried by a capacitor caused by the charge and discharge of the bus voltage1Accumulated capacity Δ Q with fault current2And keeping the two phases equal, and further determining the fault clearing time of the flexible direct current power grid under the bipolar short-circuit fault. The direct current system combines the fault removal time, the time of the direct current voltage falling to a limit point can be prolonged by changing system parameters, and the action time of the direct current protection scheme is indirectly prolonged, so that the breaker can carry out the fault removal action in longer fault processing time. Meanwhile, the flexible direct-current power grid can enable the system to have safer and more stable voltage falling margin through design parameters, the requirement of the flexible direct-current power grid on the action speed of the circuit breaker is favorably reduced, and the transient stability of the system is further enhanced.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a flowchart of a method for determining a fault clearing time of a flexible direct current power grid under a bipolar short circuit according to an embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of a bipolar short-circuit fault of a flexible direct-current power grid according to an embodiment of the invention;
FIG. 3 is an equivalent circuit diagram of the DC-side capacitor discharge according to the embodiment of the present invention;
fig. 4 is a diagram illustrating a variation of a bus voltage and a load current during a discharging process of a fault capacitor according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of "equal area principle" satisfied by the system under a fault according to an embodiment of the present invention;
FIG. 6 is a simulation model diagram of a double-ended flexible DC power grid according to an embodiment of the present invention;
FIG. 7 is a three-dimensional plot of fault clearing time with a single set of independent variable values according to an embodiment of the present invention;
FIG. 8 is a three-dimensional variation graph of the fault clearing time under the condition of a full set of independent variable values according to the embodiment of the present invention;
FIG. 9 is a graph of voltage waveforms for a simultaneous ablation fault according to an embodiment of the present invention;
FIG. 10 is a voltage waveform diagram of the system according to the embodiment of the present invention under different short-circuit fault parameters.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The method for determining the fault clearing time of the flexible direct-current power grid under the bipolar short circuit is beneficial to reducing the action speed requirement of a direct-current system on a circuit breaker and enhancing the transient stability of the system.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a flowchart of a method for determining a fault clearing time of a flexible direct current power grid under a bipolar short circuit according to an embodiment of the present invention, and as shown in fig. 1, a method for determining a fault clearing time of a flexible direct current power grid under a bipolar short circuit includes:
step 101: obtaining instantaneous values of the initial-stage voltage and current of the fault according to the initial values of the instantaneous direct-current voltage and the line current of the fault;
step 102: respectively calculating the accumulated electric quantity of the fault current and the variable quantity of the electric charge carried by the capacitor caused by the charge and discharge of the bus voltage according to the instantaneous values of the initial voltage and the current of the fault;
step 103: calculating the maximum variation of the charge carried by the capacitor during the fault according to the charge quantity carried by the capacitor at the steady-state operation point of the system and the charge quantity carried by the capacitor at the limit operation point of the system;
step 104: according to the relation between the charge quantity of the capacitor on the direct current side after the fault and the charge and discharge of the bus voltage, an equal-electric quantity principle is provided, and according to the equal-electric quantity principle, when the accumulated electric quantity of the fault current is equal to the maximum variation quantity of the charge of the capacitor during the fault, the direct current voltage operating point falls to a limit voltage point, and the fault clearing time of the system under the bipolar short-circuit fault is obtained.
When a bipolar short-circuit fault occurs in the flexible direct-current power grid, the direct-current positive electrode and the direct-current negative electrode are in short circuit, the direct-current capacitor is rapidly discharged through a fault point, the voltage drops, the current rises, and a fault equivalent circuit and a capacitor discharge equivalent circuit are shown in fig. 2 and fig. 3. At the beginning of a fault, the voltage of a direct current bus is greater than the voltage of an alternating current side line of a power grid, at the moment, the fault current mainly discharges from a direct current capacitor to a fault point, and the discharge equation of the direct current capacitor is obtained as
Figure BDA0002051292050000061
Solving a pair of conjugate complex roots of the second order differential equation:
Figure BDA0002051292050000062
in the formula
Figure BDA0002051292050000063
The instantaneous values of the initial fault voltage and current according to the initial values of the instantaneous fault direct current voltage and the initial line current are as follows:
Figure BDA0002051292050000071
in the formula
Figure BDA0002051292050000072
In step 102, the voltage of the direct current bus discharges to indicate that the charge amount carried by the capacitor is reduced, and the charge indicates that the charge amount carried by the capacitor is increased. Instant t of bipolar short circuit fault 00; fault clearing time t1(ii) a The charge quantity charged by the capacitor of the system at the steady-state operation point is Q1＝CUb(ii) a The amount of charge carried by the capacitor at the limit operating point is Q2＝CUcmax(ii) a Thereby obtaining the maximum discharge energy delta Q allowed during the fault1max。
In step 104, an "principle of equal electric quantity" in the flexible direct current power grid is further provided by analyzing the relation between the charge quantity carried by the capacitor and the charge and discharge of the bus voltage. When the flexible direct current power grid runs stably, the power of a power supply and the power of a load end of the system keep balance, namely, the input current iLWith the current i flowing through the load0Are equal. The system 'principle of equal electric quantity' can be interpreted as the accumulated electric quantity delta Q of the fault current2Equal to the maximum change Δ Q of the charge carried by the capacitor during a fault1maxWhen the DC voltage operating point falls to the limit voltage point, the fault clearing time t is up1And ensuring the system to stably operate for a fault lasting limited time.
The "equal area rule" proposed by the transient analysis of the analog AC power grid is that in the DC power grid, the variation quantity delta Q of the charge carried by the capacitor is caused by the charge and discharge of the bus voltage1Accumulated capacity Δ Q with fault current2Keeping equal, i.e., "principle of isoelectric values", as shown in fig. 4, the areas corresponding to the shaded areas D1 and D2 in the figure can be expressed as:
Figure BDA0002051292050000073
in fig. 5, the voltage U at the stable operation point of the system at the moment of failure is setbVoltage at limit operating point Ucmax. The change of the capacitance charge of the system when the system operates to the limit operating point due to the fault is expressed as:
ΔQ1max＝C(Ub-Ucmax) (7)
ΔQ1maxis DeltaQ1Maximum value of (e.g. D in FIG. 5)1Area of) of the system during a fault, Δ Q1And Δ Q2(see D in FIG. 5)2The area of) remain equal. If the two-end direct current power grid is in the fault period delta Q2≤ΔQ1The direct current system still has the capability of recovering stable operation, otherwise, the direct current system is unstable.
When is Δ Q1＝ΔQ1maxWhen the DC voltage operating point falls to the limit voltage point, the fault clearing time t is up1And ensuring the system to stably operate for a fault lasting limited time. Therefore, the DC system must be at t1The fault is removed before the moment, and the system has the transient stability operation capability. The joint type (6) and (7) can calculate the fault clearing time t1。
In step 104, combining the instantaneous fault current expression (4) in the system capacitor discharge stage, utilizing the maximum discharge energy expression (7) allowed to be released by the direct-current bus voltage to further deduce the fault removal timeTime t1。
Fault transient voltage equation, current equation and change Q of charge of capacitor from fault occurrence time to limit cut-off timemaxCan be simplified to be represented as:
Figure BDA0002051292050000081
in the formula
Figure BDA0002051292050000082
The constant g in the integral formula (8) is extracted and simplified to obtain:
Figure BDA0002051292050000083
the first partial integration of the integral formula (10) by the partial integration method is obtained:
Figure BDA0002051292050000084
and performing secondary integration on the integral term by using a fractional integration method again to obtain:
Figure BDA0002051292050000085
in the formula
Figure BDA0002051292050000086
Further analysis yielded:
Figure BDA0002051292050000091
to A4Both sides advance simultaneouslyRows are derived and simplified to:
Figure BDA0002051292050000092
combining with the formula (15), the fault limit clearing time is obtained as follows:
Figure BDA0002051292050000093
as can be seen from fig. 3, the dc bus voltage undergoes three phases of stable operation, extreme operation, and zero crossing of oscillation within a very short time after the fault. At the time of fault removal t1The front-cut fault line already uses the maximum possible discharge energy during the fault. Before the fault line is cut off, the system can still stably operate after the fault is recovered, otherwise, the voltage operating point of the system can cross the limit operating point in the transient process, and the system finally loses stability.
In summary, the maximum discharge energy allowed to be released by the DC bus voltage from the stable operation point to the limit operation point is utilized in combination with the discharge current i during the fault0Integrating the time to deduce the fault clearing time t1Comprises the following steps:
Figure BDA0002051292050000094
equation (17) gives the maximum time to process the fault t after the system fault1The limit of (2). If the flexible direct-current power grid meets the above limiting conditions after two-pole short circuit faults occur, the flexible direct-current power grid can still establish a new stable running state through a transient process after system faults occur.
Example 1
According to the invention, a simulation model of a two-end flexible direct-current power grid as shown in FIG. 6 is built in a Matlab/Simulink environment. The power supply side is connected with a VSC1 converter to be connected into a direct current power grid after a power frequency three-phase alternating current power supply is subjected to filtering and voltage transformation, and voltages at two ends of a parallel capacitor C represent direct current bus voltage. The load side is adjusted by adjusting the duty cycle of the converter VSC2 to ensure that the connected load exhibits constant power characteristics. The basic parameters of the simulation model are shown in table 1.
TABLE 1 basic parameters of Flexible DC grid
Figure BDA0002051292050000101
As can be seen from Table 1, when the system is operating stably, Ub＝500V，Ib＝40A，P020kw, line equivalent resistance RLThe dc-side parallel capacitance C is 3mF, 5.8 Ω. By the formula
Figure BDA0002051292050000102
The voltage U of the ultimate voltage operating point of the system can be obtainedcmaxIs 340V. Meanwhile, the maximum charge quantity Q allowed to be released after the system fault can be obtained by the formula (7)max＝0.48C。
As can be seen from the equation (17), the failure clearing time t1And fault line parameter R0And L0Numerical value dependent, so the examples are based on the fault line parameter R0And L0As an independent variable, the fault clearing time t1Is a dependent variable. An argument R of the set of instance data0Stepping from 1 omega to 0.1 to 5 omega, stepping from 1mh to 50mh by the independent variable L0, and calculating the dependent variable t according to the formulas (10) to (16)1The value of (c).
The set of instances is a single set of fail-over time data, i.e., the argument R in the array0And L0In a one-to-one correspondence relationship, the data obtained after each step is a set of independent variable data, and the dependent variable t is obtained1The three-dimensional change of the fault clearing time of the system under the condition of a single set of independent variable values is shown in FIG. 7.
Setting independent variable data R0Starting from 1 Ω by 0.1 to 5 Ω, R is fixed in each group0In the case of parameters, independent variable data L0Starting to step from 1mh by 1mh to 50mh, the dependent variable t can be calculated according to the equations (10) to (16)1The value of (c). From which the values of the system over the whole set of independent variables can be derivedThe three-dimensional change of the failure removal time in the case is shown in fig. 8.
Flexible direct-current power grid in given specific fault parameter R0、L0In the case of (1), the failure removal time t can be obtained from fig. 7 and 81The theoretical values of (A) are shown in Table 2.
TABLE 2 theoretical values of the fault clearing time under different parameters
Figure BDA0002051292050000103
Figure BDA0002051292050000111
Example 2
And after the flexible direct-current power grid stably runs, simulating the bipolar short-circuit fault condition of the system through the simulation model. The system is stable in running at 498V with a constant power load of 20kw at the initial time, bipolar short circuit fault occurs after 0.02s, the capacitor is discharged, and the bus voltage is reduced. The fault is removed at different times and the response of the system is shown in figure 9.
When a bipolar short-circuit fault occurs, the fault occurs at four different moments (t)a＝0.025s、tb＝0.028s、tc0.03s and td0.031s) to remove the fault and the response results are shown in fig. 9. At ta、tbAnd tcThe short-circuit fault is removed at any moment, the voltage of the direct-current bus falls to 470V, 375V and 342V respectively, the stable operation of the first two working condition systems is recovered along with the recovery of the fault, the stable operation of the third working condition system is at 360V, and the fourth working condition is that the system is at tdAnd (4) faults are removed at all times, the bus voltage drops to 335V at the moment, and the system has an unstable trend. Therefore, the fault of the flexible direct-current power grid is removed before the fault removal time, and the system can still stably operate.
Example 3
The system is in different fault parameters R0，L0In the following, the simulation changes of the DC bus voltage and the fault clearing time are as followsAs shown in fig. 10.
With system equivalent fault parameter R0、L0Change of (2), fault clearing time t1xThe simulation values of (a) are shown in Table 3.
TABLE 3 simulation values of time to failure removal under different parameters
Figure BDA0002051292050000112
Aiming at the flexible direct-current power grid with given fault parameters, the fault clearing time t obtained through simulation1xThe error results are shown in table 4, compared to the theoretical calculated values (shown in table 2).
TABLE 4 error values for time to failure removal under different parameters
Figure BDA0002051292050000113
As can be seen from table 4, under 4 different fault parameters, as the fault clearing time of the system is prolonged, the error percentage between the theoretical value and the simulation value is gradually reduced, and the accuracy of the theoretical value of the fault clearing time is continuously increased.
Meanwhile, by combining the data, after the flexible direct-current power grid fails, the time of the direct-current voltage falling to a limit point can be prolonged by changing system parameters, and meanwhile, the action time of the direct-current protection scheme is indirectly prolonged, so that the breaker can carry out fault removal action in longer fault processing time. Meanwhile, the direct current power grid can have safer and more stable bus voltage falling margin by designing system parameters according to necessary conditions required by meeting transient stability criteria, and the transient stability of the direct current system is further enhanced.
The invention provides a method for determining fault clearing time of a flexible direct-current power grid under a bipolar short circuit, which aims at the voltage stability problem of the flexible direct-current power grid, combines the transient recovery rule of direct-current bus voltage after the bipolar short circuit fault of a system, and utilizes the principle of equal electric quantity, namely in the direct-current power grid, the bus voltageThe charge variation delta Q of the capacitor caused by charging and discharging1Accumulated capacity Δ Q with fault current2And keeping the two phases equal, and further determining the fault clearing time of the flexible direct current power grid under the bipolar short-circuit fault. The direct current system combines the fault removal time, the time of the direct current voltage falling to a limit point can be prolonged by changing system parameters, and the action time of the direct current protection scheme is indirectly prolonged, so that the breaker can carry out the fault removal action in longer fault processing time. Meanwhile, the flexible direct-current power grid can enable the system to have safer and more stable voltage falling margin through design parameters, the requirement of the flexible direct-current power grid on the action speed of the circuit breaker is favorably reduced, and the transient stability of the system is further enhanced. The method for determining the fault clearing time of the flexible direct-current power grid under the bipolar short circuit is beneficial to reducing the action speed requirement of a direct-current system on a circuit breaker and enhancing the transient stability of the system.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (7)

1. A method of determining fault clearing time of a flexible dc electrical network under a bipolar short circuit, the method comprising:
obtaining instantaneous values of the initial-stage voltage and current of the fault according to the initial values of the instantaneous direct-current voltage and the line current of the fault;
respectively calculating the accumulated electric quantity of the fault current and the variable quantity of the electric charge carried by the capacitor caused by the charge and discharge of the bus voltage according to the instantaneous values of the initial voltage and the current of the fault;
calculating the maximum variation of the charge carried by the capacitor during the fault according to the charge quantity carried by the capacitor at the steady-state operation point of the system and the charge quantity carried by the capacitor at the limit operation point of the system;
according to the relation between the charge quantity of the capacitor on the direct current side after the fault and the charge and discharge of the bus voltage, an equal-electric quantity principle is provided, and according to the equal-electric quantity principle, when the accumulated electric quantity of the fault current is equal to the maximum variation quantity of the charge of the capacitor during the fault, the direct current voltage operating point falls to a limit voltage point, and the fault clearing time of the system under the bipolar short-circuit fault is obtained.
2. The method for determining the fault clearing time of the flexible direct current power grid under the bipolar short circuit according to claim 1, wherein the obtaining of the instantaneous values of the initial voltage and current of the fault according to the initial values of the instantaneous direct current voltage and the line current of the fault specifically comprises:
discharge equation based on DC capacitance
Figure FDA0003135695560000011
Solving the second order differential equation to obtain a pair of conjugate complex roots:
Figure FDA0003135695560000012
wherein
Figure FDA0003135695560000013
According to initial values of the fault instant direct current voltage and the line current, instantaneous values of the fault initial voltage and the fault initial current are obtained as follows:
Figure FDA0003135695560000021
wherein
Figure FDA0003135695560000022
In the formula, A, beta and theta are constant parameters in a fault initial-stage voltage and current instantaneous expression, sigma and w' are constant parameters in a conjugate complex root of a direct-current capacitance discharge equation, and UbAnd IbFor initial values of the fault instantaneous DC voltage and line current, R0And L0And C is a parallel capacitance value of the direct current side for fault equivalent impedance.
3. The method for determining the fault clearing time of the flexible direct current power grid under the double-pole short circuit according to claim 1, wherein the step of calculating the accumulated electric quantity of the fault current and the variation of the electric charge of the capacitor caused by the charge and discharge of the bus voltage according to the instantaneous values of the voltage and the current at the initial stage of the fault respectively comprises the following steps:
according to the formula Δ Q1＝Cuc(t1)-Cuc(t0) Calculating the variable quantity of the charges carried by the capacitor caused by the charge and discharge of the bus voltage;
according to the formula
Figure FDA0003135695560000023
Calculating the accumulated electric quantity of the fault current;
in the formula ucFor instantaneous voltage value at initial stage of fault, t0Time of occurrence of a failure, t1At the time of the fault removal, Δ i is a valid integrated value of the current during the fault.
4. The method for determining the fault clearing time of the flexible direct current power grid under the condition of the double-pole short circuit according to claim 1, wherein the maximum variation of the charge carried by the capacitor during the fault is obtained according to the charge quantity carried by the capacitor at the steady-state operation point of the system and the charge quantity carried by the capacitor at the limit operation point of the system, and the method specifically comprises the following steps:
according to formula Q1＝CUbCalculating the charge quantity carried by the capacitor at the steady-state operation point of the system;
according to formula Q2＝CUcmaxCalculating the charge quantity carried by the capacitor at the limit operating point of the system;
according to the formula Δ Q1max＝Q1-Q2Calculating the maximum variation of the charge carried by the capacitor during the fault;
in the formula of UbFor an initial value of the fault instantaneous DC voltage, UcmaxThe voltage is the limit operating point voltage, and C is the parallel capacitance value of the direct current side.
5. The method for determining the fault clearing time of the flexible direct current power grid under the bipolar short circuit according to claim 1, wherein an "equal-current principle" is provided according to the relationship between the charge quantity of the capacitor on the direct current side after the fault and the bus voltage charging and discharging, and according to the "equal-current principle", when the accumulated charge quantity of the fault current is equal to the maximum variation quantity of the charge quantity of the capacitor during the fault, the direct current voltage operating point falls to a limit voltage point, so as to obtain the fault clearing time of the system under the bipolar short circuit fault, which specifically comprises:
will fail the instantaneous voltage ucCurrent i0And the change Q of the charge of the capacitor from the time of occurrence of the fault to the time of limit cut-offmaxThe simplified representation is:
Figure FDA0003135695560000031
wherein
Figure FDA0003135695560000032
In the formula, A, beta and theta are constant parameters in a voltage and current instantaneous expression in the initial stage of the bipolar short-circuit fault of the flexible direct-current power grid, and U isbAnd IbInitial values of the direct current voltage and the line current at the moment of the fault; obtaining the conjugate complex root as lambda1,2＝-σThe dc capacitance discharge equation of ± jw' is:
Figure FDA0003135695560000033
wherein R is0And L0C is the dc side parallel capacitance value, which is the equivalent impedance in the fault circuit.
Will be the equation
Figure FDA0003135695560000034
After the relevant fractional integral conversion is carried out, the fault clearing time of the system under the bipolar short-circuit fault is obtained as follows:
Figure FDA0003135695560000041
in the formula
Figure FDA0003135695560000042
6. A system based on the method for determining the fault clearing time of the flexible direct current power grid under the condition of the double-pole short circuit is characterized by comprising a power frequency three-phase alternating current power source, wherein an output end of the power frequency three-phase alternating current power source is connected with a direct current bus through an alternating current breaker, a filter, a transformer and a power type converter VSC1 in sequence, and the direct current bus is connected with a direct current load through a power type converter VSC 2.
7. A system for determining the time of fault removal of a flexible direct current grid under a double short circuit according to claim 6, characterised in that the source converter VSC1 is a unidirectional AC/DC converter and the source converter VSC2 is a bidirectional DC/DC converter.
CN201910374908.1A 2019-05-07 2019-05-07 Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit Active CN109980595B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201910374908.1A CN109980595B (en) 2019-05-07 2019-05-07 Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201910374908.1A CN109980595B (en) 2019-05-07 2019-05-07 Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit

Publications (2)

Publication Number Publication Date
CN109980595A CN109980595A (en) 2019-07-05
CN109980595B true CN109980595B (en) 2021-10-08

Family

ID=67072994

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201910374908.1A Active CN109980595B (en) 2019-05-07 2019-05-07 Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit

Country Status (1)

Country Link
CN (1) CN109980595B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110571766B (en) * 2019-07-23 2020-11-13 中国南方电网有限责任公司超高压输电公司检修试验中心 Direct-current line fault restarting method

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107565590A (en) * 2017-09-06 2018-01-09 合肥工业大学 The mixed high-voltage DC transmission system sent outside suitable for wind-powered electricity generation

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3808624B2 (en) * 1998-04-21 2006-08-16 株式会社東芝 System protection relay device
KR100943438B1 (en) * 2005-07-29 2010-02-19 아메리칸 수퍼컨덕터 코포레이션 Fault management of HTS power cable
CN103066573B (en) * 2012-12-13 2015-01-21 国网智能电网研究院 Modular multi-level multi-terminal flexible direct current system direct current fault handling method
US10355585B2 (en) * 2015-03-12 2019-07-16 Eaton Intelligent Power Limited Variable frequency drive circuit with overvoltage protection
CN104953568B (en) * 2015-07-17 2017-11-07 江苏雪梅制冷设备有限公司 A kind of fault protecting method of flexible direct current power transmission system
JP6438453B2 (en) * 2016-12-21 2018-12-12 ファナック株式会社 Motor drive device

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107565590A (en) * 2017-09-06 2018-01-09 合肥工业大学 The mixed high-voltage DC transmission system sent outside suitable for wind-powered electricity generation

Also Published As

Publication number Publication date
CN109980595A (en) 2019-07-05

Similar Documents

Publication Publication Date Title
CN110034533B (en) Method for determining transient stability criterion of flexible direct-current power grid under disturbance fault
CN101789600B (en) Method for controlling dynamic direct voltage of parallel connection type active electric filter
CN103500261B (en) Method for fault simulation of direct
CN108808718B (en) Method for determining direct current operation range of high-voltage direct current transmission system in alternating current fault
CN112701710B (en) Energy storage converter stability control method based on alternating current constant power load dynamic performance
CN106961115B (en) High-voltage direct-current power transmission system equivalent current voltage source modeling method and model
CN106230296A (en) In grid-connected test power supply, method is analyzed in the control of inverter
CN106374488A (en) Fractional order terminal sliding mode-based AFNN control method of active power filter
CN104868762B (en) A kind of electric power electric transformer and its control method of scattered energy storage
CN108120878B (en) Direct current resistance selection method and system of complex power distribution network comprehensive optimization device
CN106981865A (en) A kind of two-way AC/DC converters control method for parallel connection system of direct-current grid
CN104993494B (en) Motor simulator based on four-quadrant power electronic converter and method
CN110503214B (en) Additional electric quantity-based method for transient stability recovery control of voltage of direct current power grid
CN105048821A (en) Load current feedforward control method of increasing full-bridge isolation DC-DC convertor output voltage dynamic response
CN103441502B (en) Parallel single-phase H-bridge cascade type active electric power filter and method thereof
CN105978373A (en) Three-phase inverter backstepping sliding mode control method and system for achieving stabilization of micro-grid
CN114884078A (en) High-voltage direct-hanging system integrating reactive compensation and energy storage
CN109980595B (en) Method for determining fault clearing time of flexible direct-current power grid under bipolar short circuit
CN104734537A (en) Control method for wind power current converter based on positive-and-negative sequence current inner-loop control
CN102684204B (en) Cascading-type STATCOM DC side capacitor voltage balance control method
CN103117562A (en) Control method of high-voltage cascade energy feedback converter power module
CN112952867A (en) Method for suppressing output voltage unbalance of energy storage power converter under asymmetric load
CN110880794B (en) Power distribution method and device of hybrid energy storage virtual synchronous generator
CN204497970U (en) A kind of transless cascade multilevel converter electric capacity pre-charge circuit
CN206323163U (en) A kind of equivalent idle battery circuit

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant